Recently, smart phones or tablet personal computers (PCs) have become widely spread, and techniques for contact position measurement devices included therein have been actively developed. A smart phone or tablet PC usually includes a touch screen, and a user may designate specific coordinates on the touch screen by using a finger or a pen. The user may input a particular signal to the smart phone by designating particular coordinates on the touch screen.
The touch screen may operate based on an electric scheme, an infrared scheme, and an ultrasonic scheme, and an example of the electric scheme may include a resistive (R)-type touch screen or a capacitive (C)-type touch screen. Conventionally, R-type touch screens are mostly used, and is capable of simultaneously recognizing a user's finger and a pen, but the R-type touch screen has a problem that a reflection is caused by an air layer between indium tin oxide (ITO) layers. More specifically, due to the air layer between the ITO layers, transmittance of light transmitting from a display is degraded, increasing external light reflection.
Thus, nowadays, C-type touch screens have been popularly used. C-type touch screens operate in a way such that they sense a change in a capacitance of a transparent electrode occurring due to the contact of an object. However, C-type touch screens have an operation error resulting from unintended contact of a hand using a pen because the hand and the pen are difficult to physically distinguish from each other.
Conventional techniques for solving this problem may include processing with software that distinguishes a hand from a pen based on a contact area, using a separate location measurement device such as an electromagnetic resonance (EMR) type in addition to the C-type touch screen, and so forth. The techniques may also include an electrically coupled resonance (ECR) type to receive an electric field from the pen in an electrode and measure the location of the pen.
Unlike a passive pen technique like an EMR pen or an ECR pen, an active pen technique uses an included power source.